An organic electroluminescence (referred to as organic EL hereinafter) display is a self-luminous type display and has advantages for example that the organic EL display is thin and lightweight and consumes less power. Therefore, the organic EL display has been actively studied and developed in these years for use as a display device such as FPD (flat panel display).
The driving scheme for the organic EL display is categorized into the passive matrix scheme and the active matrix scheme. The passive matrix scheme drives organic EL devices (OLED devices) line by line using stripe-arranged scanning electrodes and stripe-arranged data electrodes orthogonal to the scan electrodes. The active matrix scheme provides a switching transistor (select transistor) and a driving transistor at each pixel for driving organic EL devices (OLED devices). Since the active matrix scheme can control current for each pixel and is accordingly advantageous in terms of reduction of the power consumption of the organic EL display and extension of the lifetime of the organic EL devices.
In the conventional active-matrix-driven organic EL display as described above, a silicon-based semiconductor material such as amorphous silicon (a-Si) or polysilicon (poly-Si) is used in most cases as a material for an active layer of the switching transistor or driving transistor used in the organic EL display. Recently, instead of the silicon-based thin-film transistor (TFT), an organic TFT using an organic semiconductor material or TFT using a transparent semiconductor such as ZnO has been proposed. For example, Japanese Patent Laying-Open No. 2003-255857 (Patent Document 1) and Takashi Chuman et al., “PIONEER R&D”, Vol. 15, No. 2, Aug. 31, 2005, pp. 62-69 (Non-Patent Document 1) each disclose a hybrid organic light-emitting transistor including an organic EL device and an organic TFT device arranged on the same substrate in which an organic semiconductor material such as naphthalene or pentacene is used for an active layer of the organic TFT. In the active-matrix-driven organic EL display using the organic TFT, the organic TFT and the organic EL device can be formed on a plastic substrate for example. Thus, a flexible and lightweight organic EL display using such an organic TFT and an organic EL device is expected to be realized.
The hybrid organic light-emitting transistor including an organic EL device and an organic TFT device arranged in parallel on the same substrate as disclosed in the above-referenced documents, however, has the problems for example as described below. First of all, in the conventional hybrid organic light-emitting transistor as described above, different organic materials are used for respective active layers of the organic TFT device and the organic EL device. Therefore, a shadow mask of SUS or the like is necessary in the process of forming each device. At this time, a large alignment margin has to be secured in consideration of the precision in mask alignment. In particular, the recent increase in screen size of the display is accompanied by the increased substrate size, a larger substrate leads to a more noticeable displacement of the shadow mask particularly near the end face of the substrate, because of a difference in thermal expansion coefficient between glass commonly used as a material for the substrate and SUS used as a material for the shadow mask, and therefore, a sufficiently large margin is required. It is accordingly difficult to make the pixel smaller, enhance the resolution and increase the screen size of the display. Further, because of the required larger alignment margin in consideration of misalignment of the shadow mask, a larger device isolation width (distance between the organic EL device and the organic TFT device) is accordingly required, resulting in a problem that the ratio of the light emitting element (organic EL device) area to the pixel area (aperture ratio) cannot be increased. Furthermore, because the shadow mask contacts the surface where the device is formed, dust is likely to be generated due to the contact, resulting in a problem of deterioration in yield.
Moreover, the organic EL device and the organic TFT device have to be produced in separate process steps, resulting in a problem that the manufacturing process is complicated.
Patent Document 1: Japanese Patent Laying-Open No. 2003-255857
Non-Patent Document 1: Takashi Chuman et al., “PIONEER R&D”, Vol. 15, No. 2, Aug. 31, 2005, pp. 62-69